1. Field of the Invention
The present invention relates to an image forming apparatus and image forming method, and more particularly, to an image forming apparatus and image forming method that increase the useful life of the image carrier and improve the image quality by supplying a lubricant to the image carrier.
2. Description of the Related Art
An image forming apparatus of the conventional art using the electrophotographic method, such as a copier or printer, uniformly charges the surface of an image carrier (e.g., a photoreceptor drum) using a charger and forms an electrostatic latent image thereon by exposing the image carrier with light modulated based on the image. The formed electrostatic latent image is developed using toner into a toner image, which is then transferred to a recording medium or to an intermediate transfer unit and then to a recording medium, and the transferred toner image is heated by a fusing device such that it fuses to the recording medium, thereby forming a final image.
Image forming apparatuses of this type include a cleaning device that removes and cleans off the residual toner from the photoreceptor after the toner image formed on the image carrier (e.g., a photoreceptor drum) or the intermediate transfer unit (hereinafter referred to as an ‘image carrier’) is transferred to the recording medium.
The cleaning device is often of the type in which a cleaning blade is brought into contact with the image carrier surface to scrape off the residual toner. However, using this construction, substantial friction between the cleaning blade and the image carrier shaves away the photosensitive film on the image carrier surface and/or wears down the cleaning blade, causing a reduction in the useful lives of both component members.
As a countermeasure against this problem, a technology is known whereby a lubricant is applied to the image carrier surface to reduce the frictional coefficient thereof, thereby preventing wear on the cleaning blade and damage to the photosensitive film on the image carrier surface and extending the useful lives of the component members. However, this technology entails the problem that when the residual toner is removed using a cleaning blade, the toner that has been scraped off adheres to and remains on the blade edge, and the lubricant applied to the image carrier surface is scraped off by the residual toner.
Accordingly, a method has been proposed in which an application brush is used to carry solid lubricant, which is then applied to the image carrier surface by bringing the application brush into contact therewith. For example, according to Japanese Patent Application Laid-Open No. 2002-244486, the degree by which the application brush is pushed into a solid lubricant and the rotation rate of the application brush are controlled based on information regarding the cumulative drive time of the image carrier sought from the cumulative number of prints as well as on the counter value for the number of dots in the image, which indicates the black/white ratio.
Japanese Patent Application Laid-Open No. 7-311531 proposes a technology in which the amount of lubricant applied to the surface of the image carrier is detected, and based on the detection result, the rotation of the application brush is controlled to be ON or OFF, or the rotation rate of the application brush is controlled.
However, using an image forming apparatus of the conventional art described above, such information as the image carrier cumulative drive time and the counter value for the number of effective dots in the image (which indicates the black/white ratio) must be collected and processed, or means to detect the amount of lubricant applied to the image carrier surface and control the rotation of the application brush are needed, which makes the construction of the apparatus complex and increases the manufacturing cost.